It is known that moisturization of the skin remains one of the major objectives of cosmetics. A variety of active ingredients are used for this purpose. They belong to two major categories: the first category comprises low-molecular compounds and the second category comprises high-molecular substances. The first family can have a high moisturizing capacity over a relatively short time, whereas the effect in the case of the second family is less substantial although longer-lasting. Examples of the low-molecular moisturizing substances which may be mentioned are glycerol, urea and the constituents of the natural moisturizing factor (or NMF). The high-molecular moisturizing substances, which are generally of the polymeric type, comprise in particular certain proteins such as collagen.
It is further known that the intercellular cement of the stratum corneum consists of a hydrophobic complex group of lipids made up essentially of free steroIs, free fatty acids, triglycerides, glycosphingolipids and ceramides. The hydrophilic molecules used as moisturizers will be repelled by this hydrophobic medium and will have to find their way to the lower layers of the epidermis and especially to the dermis, which contains a large amount of water. Thus the stratum corneum and the upper layers of the epidermis will be influenced very little by moisturizing substances. Now, the impression of dryness of the skin comes from the stratum corneum and the upper layers of the epidermis. It therefore proves important to be able to keep the moisturizing molecules used for as long as possible in these layers.
Document JP-B-46-9327 has described a process for the manufacture of a fatty acid ester of chondroitin sulfate by reacting a fatty acid halide with the free hydroxyl groups in the saccharide part of the chondroitin sulfate. However, the proportion of fatty acid in the reaction product obtained is low. This reaction product does not possess significant moisturizing properties and even less an emulsifying activity. Other similar documents are JP-A-17 566/68, JP-A-02/169684, JP-A-62/238209 and JP-A-02/243611. Document US-A-4 223 023 describes a binder for non-absorbable lipids which is based on chitosan, in particular in the form of fatty acid/chitosan complexes by neutralizing chitosan with fatty acids (column 1, lines 42 to 48). This product is applied as a lipid binder and in particular as a fat extender in margarines and sauces, especially salad dressings (page 2, lines 37 to 41). This product also reduces the calorie contents of the foodstuff (page 2, lines 33 to 36).
NOVAK U.S. Pat. No. 2,749,276 and GILLETTE French Patent FR-A-2,009,161 disclose covalent esters of fatty acid and polyose prepared in an organic medium at a high temperature which are soluble in organic solvents due to a very high content in covalently bond fatty acid groups. This reaction products with a high covalent content in fatty acid groups do not have emulsifying or moisturizing properties.
In the prior art U.S. Pat. No. 2,749,276 and French patent 2,009,161, the proportion of the fatty acid groups linked through covalent bonds with the polyose is ranging between 40 and 80% which impedes that such a product has an emulsifying power, said reaction product having lost the hydrophylic character of the polyose.